This calculator is quite good, the CBCPW calculation is the best I have found.
Here a screen shot of the microstrip calculation.
For microstrip calculations, the Effective Dielectric Constant is derived from a combination of the resin, glass and air. It does not include the effects of soldermask. However it good enough to get you within 50 ohms +/- 5%.
Phase Constant
Phase Constant sounds like something complicated, until you realize it's nothing more than angular rotation of phase in degrees of a sine wave for a selected unit of length.
In the screen shot above I intentionally manipulated the Dielectric Constant (Er) while keeping the electrical length set to 360 degrees until the phase Constant equaled 60 degrees.
As shown the Physical length of the microstrip at 1GHz wtih a dielectric constant of 5.62213 equals 60 degrees per inch. So 6 inches = 360 degrees (6 x 60 = 360). Pretty simple math.
Critical Length
We have often heard about the term critical trace length for high speed and RF designs. Most often you hear numbers like 1/7 or 1/10 of a wavelength as being the critical trace length.
The critical trace length is simply the length at which you must use a good transmission line to send transmit and receive signals and on your PCB.
Digital circuit designers are familiar with Rule of Thumb #1 Bandwidth of a signal from its rise time.
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